2%) and the growth rate slowed during the middle and later stages; ?During the prior stage, Beijing experienced two periods with heavy air pollution days as a result of the local accumulation of pollutants, secondary transformation, and regional transport. The concentration of PM2.5 in February was nearly 60% lower than in February 2014 under similar meteorological conditions in Beijing; ? Following an increase in traffic volume and industrial activity, changes in air pollutants tended to be stable or slightly increase during the middle and later stages of the control period. The grey relation coefficients between thermal radiation intensity anomalies and the main pollutants in heavy industrial cities were greater than 0.6, which means that the control of industrial emissions remains key to controlling air pollution.With the rapid development of industry, chromium (Cr) has become one of the main soil heavy metal pollutants in China, seriously affecting the soil ecological environment and health of residents. In this study, contaminated soil samples were taken around the tannery sludge yard area in Heibei Province. The Illumina MiSeq high-throughput sequencing technology was employed to analyze the structure and assembly processes of soil bacterial communities at different pollution levels. Results showed that chromium pollution significantly influences soil properties and soil bacterial communities. The composition and structure of bacterial communities were significantly shifted at different pollution levels. Furthermore, the α diversity of bacterial communities may decrease with relatively high concentrations of chromium. Bacterial communities in chromium polluted soil can be divided into 55 phyla, where Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, and Firmicutes are the dominant phyla (relative abundance&gt;5%). Moreover, the soil bacterial communities were dominated by the deterministic assembly process (homogeneous selection) and the stochastic ratios decreased with increases in the concentration of chromium in soil. The total concentration of chromium, soil moisture, pH, and organic matter were significantly correlated (P less then 0.05) with the bacterial communities. Therefore, these soil properties might be the driving factors affecting the structure of bacterial communities.Rice is well known to accumulate methylmercury (MeHg) and the consumption of rice in mercury (Hg) polluted areas has been confirmed to be a primary source of MeHg exposure. https://www.selleckchem.com/products/gsk2578215a.html Therefore, how to inhibit the formation and accumulation of MeHg in the paddy field system needs to be solved urgently. Chitosan modified biochar, a potential inhibitor, was selected in this study to explore its effect on MeHg production and accumulation in the paddy field system by analyzing the mercury content of interstitial water, soil, and rice plant tissues. The results showed that the addition of chitosan modified biochar could significantly reduce MeHg concentration in the soil with the decreased methylation rate of 51.1%-79.1%, and could also decrease the total mercury (THg) and MeHg content of interstitial water. At the maturation stage of rice, the MeHg content of rice roots treated with chitosan modified biochar (CMBC) was 73.1% lower than without biochar (CK1) and 62.0% lower than with unmodified biochar (CK2), and the rice MeHg was 75.8% lower than that of CK1 and 72.9% lower than that of CK2. In addition, the application of biochar could promote the growth of rice with the plant biomass of CMBC and CK2 of 1.6 and 1.7 times higher than that of CK1. Generally, the application of chitosan modified biochar into paddy soil could not only promote the growth of rice, but also inhibit the accumulation of MeHg in rice, suggesting that the chitosan modified biochar has a certain application value in the inhibition of the MeHg formation and accumulation in paddy field system.An incubation experiment was conducted to explore the influence of 30% water holding capacity (WHC), flooding, and alternate dry-wet conditions on changes in heavy metal fractions with 1% rice straw biochar in Pb and Cd co-contaminated paddy soils, to provide a scientific basis for a water regime of biochar remediation on heavy metal contaminated paddy soil. Results showed that flooding and alternating wet-dry conditions could significantly increase soil pH, the contents of dissolved organic carbon (DOC), and amorphous iron oxide (Feo) after adding biochar. Compared with a 30% WHC treatment, when the soil is flooded and alternating wet-dry conditions, the content of the TCLP extractable Pb decreased by 31.87% and 20.33%, respectively, and the content of the TCLP extraction Cd decreased by 25.29% and 16.07%, respectively. Under flooding, the acid soluble Pb and Cd content decreased by 24.78% and 20.14%, respectively, and the acid soluble Cd content decreased over time. The decreasing order of available Pb and Cd content was flooding &gt; alternating dry-wet &gt; 30% WHC. Correlation analysis results showed that soil pH and Feo have significant negative correlation with available heavy metals, which means flooding with biochar could effectively immobilize Pb and Cd by increasing soil pH and Feo content. Flooding and biochar have a synergistic interaction on promoting the transformation of Pb and Cd to more stable fractions in acidic co-contaminated heavy metal polluted paddy soil.A pot experiment was conducted to investigate the growth response and Cd accumulation characteristics among different populations of Hylotelephium spectabile in Cd-contaminated cinnamon soil (2.22 mg?kg-1) with the addition of different concentrations of NaCl. Results showed that the biomasses and Cd concentrations of H. spectabile showed significant differences among different populations under Cd alone or Cd-salt combined stress. Moreover, salt stress aggravated the growth inhibition of H. spectabile and the Cd concentrations in different H. spectabile populations showed a declining trend, which may be related to the salt-derived pH increase leading to a decrease in Cd bioavailability. In addition, the growth and Cd absorption responses of H. spectabile under salt stress were significantly different in the different populations. The shoot biomasses of the LN population were significantly higher than in other populations under different treatment, and showed no significant decrease with the addition of 1% NaCl when compared with the control treatment and the tolerance index remained 0.